In general, a diverter generates lateral reaction force to steer a rocket, missile, and other projectile in flight. The amount of impulse generated by the diverter will determine how much the flight path is diverted. Impulse is the product of the average reaction force over the time exerted.
Recent applications for diverters include steering 2.75-inch diameter rockets, artillery, and gun projectiles, e.g., 30 mm projectiles. In such applications, we need small diverters that can generate relative high impulse (e.g., 1 to 5 N-sec) in short time periods. Because rockets, missiles, and projectiles often spin at high rates, the impulses must be made in a short time period, e.g., on the order of 1 ms. If, for example, a projectile is spinning at 3600 RPM, it is spinning at 60 revolutions per second or 21.6 degrees per millisecond. If the diverter provides a reaction force for 10 ms, this will provide force over 216 degrees. Providing the force over this time period is not efficient. Instead, we would like to provide the force for 1-ms or less. If the diverter can provide the force over this shorter period, the guidance system can make multiple steering corrections when needed as a projectile flies through space by igniting the multiple diverters arranged around it.
One might consider using small rocket motors for diverters having small volume, but this has proven ineffective when a relatively high impulse is required over a short time. It is too difficult for a rocket motor with loose loaded propellant to burn all of its propellant in a short time without ejecting a large percentage of the propellant unburned. Further, the relatively low packing density of propellant results in the rocket motor ejecting a considerable volume of propellant. Additionally, the rocket propellant container cannot be manufactured that small. Providing the propellant in a higher density form, e.g., cast propellant grain, might appear helpful, but a compact single grain is unlikely to have a thin enough web to operate in the required time period due to propellant burn rate limitations. Where low cost is required, such as less than $5.00 per diverter, without large capital investment, it is difficult to envision good results with rocket motors. Small rocket motors can provide impulses of 1-5 N-sec, but for longer time periods on the order of 10 milliseconds. Additionally, rocket motors are not volume efficient for another reason. To fully use the energy in a rocket propellant, a converging/diverging nozzle with significant mass and volume is needed to fully expand and accelerate the propellant gas.
Another approach might be to use conventional bridgewire pyrotechnic devices for small diverters, but there are unsolved problems. One problem is how to ignite them quickly and reliably. Conventional semiconductor bridge technology provides very fast hot ignition, but it is also only low energy ignition lasting for microseconds. The energy output is dependent on energy input; when only low input energy is available, only small output energy can be produced, which may not be sufficient to provide reliable ignition. Further, conventional pyrotechnic devices and semiconductor bridges require tight coupling between the ignition element and the pyrotechnic material. Up to now it has been critical for reliable ignition with semiconductor bridges that the ordnance or pyrotechnic material to be ignited be in close contact with the semiconductor bridge during ignition. This means lower ignition energy can be used, but it requires intimate contact between the bridge and prime, adding to manufacturing costs. The applications mentioned earlier can subject diverters to very high accelerations and shocks, e.g., on the order of 100,000 g's. During such events the prime may separate from the ignition element and reduce the reliability of the diverter. Bridgewires require high firing energies or very small and unsafe bridgewires for fast response. Thus, attempts to produce small low cost diverters generating relatively high impulse over brief periods of time have not been successful.